Can 'combined' speeds exceed the speed of light?

Question

Lets say two objects are traveling at 60% of the speed of light and traveling away from each other. From simple math, the relative combined speed from either of the objects would be 120%. I understand that the objects mass would be greatly increased, even at 60%, but wouldn't it be possible?

Answer 1

This question you're posing is a popular question to try to disprove Einstein. However, unfortunately, Einstein's formulas make use of the Lorentz transformations, which account for this and still prevent the speeds from exceeding c, the speed of light. Einstein discovered a velocity addition formula. Velocities do not simply add as you might expect with the case of two cars going away from each other each at 60mph. Instead, you have to adjust for a factor that still prevents the speeds from approaching c, creating a mathematical limit. The formula is (v + w) / (1 + vw/c^2) where v and w are the two speeds you're adding, and these are the speeds relative to each other, that is what one car perceives as the other car's speed and vice versa. (At low speeds like 60mph, the factor becomes too tiny for us to detect and so the two cars will indeed see the other as going 120 mph.)

Rather than try to explain it, wikipedia has an excellent explanation; here's the page:

http://en.wikipedia.org/wiki/Speed_of_light

Somebody wrote:
> However, they are not either one going over 60 MPH. The speed has to be relative to a fixed point to count as 'faster than light'.

Be careful here. Einstein taught us there there are no fixed points in the universe, none whatsoever; instead, every speed is relative. Prior to Einstein, they believed in the ether, which had fixed points. (However, technically, Einstein didn't disprove the existence of the ether; rather, he showed it does not apply to the formulas and that mathematically it doesn't need to exist.)

Answer 2

Two cars speeding away from each other at 60 MPH have a combined speed of 120 relative to each other. However, they are not either one going over 60 MPH. The speed has to be relative to a fixed point to count as 'faster than light'. They did not know if the sound barrier could be broken, but it was. Theoretically, you could not talk on a plane going faster than sound, your voice should just fall on the floor. Since your voice is going out, relatively to your fixed body, at the speed of sound it can be heard. Relative to the ground, the sound waves should be traveling much faster than the speed of sound, but it's not like someone on the ground could have heard you anyway.

Faster than light travel is most likely possible, but it is not in the new future. We do not have the switching technology yet to make a successful ion drive.

Answer 3

In theory, I guess the two particles would be traveling faster than the speed of light relative to each other. However, any object not moving that one of the objects might be traveling towards obviously would make the object seem like it is moving slower. I think this has to do with Einstein's Theory of Relativity.

In simple terms, I guess it is possible but only for the two objects in motion.

Answer 4

This is why physics professors invest in painkillers. OK, yes, relative to each other the objects are moving apart faster than c. But this is the weird part. If you were on one object, looking at the other, you would still be 'seeing' the other object, with real photons moving at c, but the energy would be lower than what was actually emitted. What was given off as visible light at one object might only be detectable as radio waves at the other. The relative mass of the objects does not affect this distortion, called 'redshift', only the relative speed.

Answer 5

Because of the equivalence of energy and mass, the energy which an object has due to its motion will add to its mass. In other words, it will make it harder to increase its speed. This effect is only really significant for objects moving at speeds close to the speed of light. For example, at 10 percent of the speed of light an object’s mass is only 0.5 percent more than normal, while at 90 percent of the speed of light it would be more than twice its normal mass. As an object approaches the speed of light, its mass rises ever more quickly, so it takes more and more energy to speed it up further. It can in fact never reach the speed of light, because by then its mass would have become infinite, and by the equivalence of mass and energy, it would have taken an infinite amount of energy to get it there. For this reason, any normal object is forever confined by relativity to move at speeds slower than the speed of light. Only light, or other waves that have no intrinsic mass, can move at the speed of light.

Answer 6

Yes, by blatantly adding the speeds your number would be faster than the speed of light. But in reality the physics become pretty distorted the closer you actually get to the speed of light. One would need an infinite amount of energy to accelerate to the speed of light let alone past it, due to the increase in mass. That's why people talk about wormholes, etc. Those would be non-conventional forms of travel, thus (hopefully) subject to non-conventional physics.

Answer 7

Your fatal error lies in this line,
"say two objects are traveling at 60% of the speed of light and traveling away from each other."
What, if anything, are you using as a reference point to measure these two speeds?
There is no such thing as an absolute speed....everything must be measured with some type of reference point.

Lets say that the two speeds measured were with respect to some unmentioned observer who we will say has a velocity of zero with respect to himself.
In this case, the two objects are each traveling at 60% c with respect to the observer, neither is traveling faster than the speed of light in this reference frame.

But what about someone on one of the objects measuring the speed of the other object?
Even in this case, faster than light travel is impossible.
When dealing with relativistic speeds, you cannot simply add them together to get the relative speed.

See this page for adding relativistic speeds together,
http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/einvel2.html

No matter how fast the two objects are traveling away from each other as measured by some outside observer, with respect to each other, they will never be moving apart faster than the speed of light.

Answer 8

just because you combine speeds of an object does not mean it will increase in speed! its actuly the opposite! the faster an object travels the more mass it assumes! unless said object is traveling in a vaccum!

Answer 9

Well combined speed of all cars on Earth traveling at one time might be over the speed of light. What are you getting at?

Answer 10

Hi
the answer is no

First what you need to understand is what happens to objects when they try to reach light speeds. Okay

Have you tried to push a car ( in neutral of course) from a stop position to a moving one? When you tried to move it, it opposed you from moving it for a time. until you finally got it moving this resistance is called interia and let say you tried to push it faster while it still moving. Again the car opposed your effort to move it from a slower speed to a higher one. Interia is what prevent this from happening Also it take energy to move it from one speed to other. Inerita happen to any object with mass. At ordinary speed we deal with. we can change our object speeds. Be it car, plane, train, bike , whatever. with the application of energy with some difficulty but we can do it. However as you started approaching the speed of light your trying to move the object in very geat distance in a very very short time and the object is going to oppose you from doing it. So it more energy to move it. To reach light speed it would take infinite energy which this universe does not have to get you there. To go faster you who need more than inifinite power which is impossible for this universe to supply. So nothing with mass can go faster than the speed of light in this universe . expect light for the reason that photons have no mass. so there no resisted by Inerita

Hope this answer your question?